The present disclosure relates to a self-regenerating particulate sensor, and more particularly, to a self-regenerating sensor capable of detecting particulates emitted from an exhaust gas. Incomplete combustion of heavy hydrocarbon compounds, such as heavy oils, diesel oil, and the like leads to particulate formation. In the operation of internal combustion engines, xe2x80x9csmokingxe2x80x9d of the engine leads to ambient air pollution although the carbon monoxide and hydrocarbon emission of the exhaust gases from the internal combustion engine itself are very low. It is, therefore, desirable to detect the formation of particulates in the exhaust of the engine and to provide an output signal that can then be used to indicate the presence of particulates and further to be used as a sensing or control signal, for example in a control loop, to automatically adjust air, or the supply of fuel for complete combustion and to prevent excess particulate formation.
Currently exhaust gases can be sensed by optical sensors; however, such sensors are more suited to fixed locations, for example smokestacks, and are not readily adaptable to automotive use, particularly in view of the rugged and highly variable ambient operating conditions associated with automotive use, including wide swings in temperature, temperature gradients, shock, vibration, and the like. It would, therefore, be desirable to provide a more robust sensor capable of directly sensing exhaust particulates.
In the past, a sensing plate has been used for detecting exhaust particulates, wherein the sensing plate changes the electrical conductivity of a sensor by the formation of a carbon bridge between electrodes. To refresh the sensor, the deposited particulates are burned off by means of a catalyst with extra oxygen in the engine exhaust. Such sensors, however, are not completely practical because the strong reduction effect of the particulates can damage the electrode and detach the electrode from the sensing plane. Current sensors are furthermore unable to control both the temperature surrounding the sensor and the rate of the exhaust flow. This inability is disadvantageous as it allows for the condensation of humidity or moisture on the sensor, which leads to the gradual deterioration of the sensor; thus preventing the sensor from controlling the particulate deposition process, which in turn prevents the sensor from being a direct mechanism by which particulates may be removed from the exhaust. A further problem with current sensors is that they are primarily limited to use with direct current methods of sensing conductivity. Such methods are problematic in that the electrical properties are highly non-liner, thereby making it difficult to control the rate of exhaust flow.
Disclosed herein is a particulate sensor system, comprising a non-ionically conductive substrate, a non-ionically conductive porous protective layer, a heater, a first sensing electrode and a second sensing electrode; the first and second sensing electrodes being in thermal and electrical communication with the heater; the first and second sensing electrodes being disposed on the same side of the substrate; and the porous protective layer disposed on the electrodes on a surface of the electrodes that is sensing particles.
Further disclosed is a method for operating a particulate sensor system comprising introducing a gas stream to a sensor; monitoring the resistance between the first sensing electrode and the second sensing electrode, and increasing the temperature of the sensor when the resistance is greater than or equal to a first selected level.
Further disclosed is a method for operating a filter system comprising exposing a sensor to a pre-selected number of self-regeneration cycles, and increasing the temperature of the filter system.